A position indicator is gripped by a user and used for position indication on a sensor of a position detection apparatus. The position detection apparatus detects the position of a sensor electrode that is electrically coupled to the position indicator to detect the indication position by the position indicator on the sensor of the position detection apparatus. As a method for detecting electric coupling between the sensor and the position indicator, various methods are known including a method for detecting capacitive coupling and a method for detecting electromagnetic coupling.
It is conventionally done to provide, in a position indicator of the type described, a light emitting element configured, for example, from a light emitting diode (LED) such that the light emitting element is controlled to emit light in response to various applications.
As uses of a position indicator in which light is emitted, confirmation of a manipulation of a power supply switch (for example, Patent Document 1 (Japanese Patent Laid-Open No. 2011-18090)), illumination on a pen tip from a light emitting element provided in the proximity of the pen tip (for example, Patent Document 2 (Japanese Patent Laid-Open No. 1999-184633)), and so forth are known. Since to cause a light emitting element to emit light is high in visibility to a user, this is utilized in various uses in addition to such confirmation of a manipulation or illumination as described above.
Incidentally, a power supply for driving a light emitting element in a position indicator to emit light is generally configured such that a primary cell is provided on the position indicator or a secondary cell or an electric double layer capacitor is provided to charge the position indicator through a charger. However, the method that uses a cell as the power supply to a light emitting element has a fundamental problem that, if the cell is placed into a cell exhaustion or charging shortage state, then a necessary power supply voltage cannot be obtained from the cell.
As a method for avoiding this problem, Patent Document 1 and Patent Document 2 disclose that a coil for receiving power and an accumulation circuit are provided in a position indicator and an electromagnetic wave is sent from a position detection apparatus to the position indicator to allow the position indicator to generate a power supply voltage through electromagnetic induction.
For example, Patent Document 3 (Japanese Patent Laid-Open No. 2005-010844) discloses, as a position indicator that uses an electromagnetic coupling method as a coupling method for position indication to a sensor of a position detection apparatus, a position indicator that includes a resonance circuit configured from a coil and a capacitor such that an alternating-current (AC) signal from the sensor of the position detection apparatus is received by the resonance circuit and the received AC signal is fed back from the position indicator to the sensor of the position detection apparatus to allow the position detection apparatus to detect the indication position by the position indicator. Further, it is disclosed that, in the position indicator of Patent Document 3, an electromagnetic wave from the position detection apparatus is received by a resonance circuit configured from a coil and a capacitor and a power supply voltage in the position indicator is generated from the received signal power.